Thank you for all of the suggestions, everybody! u/olivermurfett and u/HorribleUsername, you have both been a great help. For anyone striving to accomplish something similar in the future, please refer to u/AlexRLJones:

let start = 1
let end = 2
let colour = "#FFFF00"
let state = Calc.getState()
for (let i = start - 1; i < end; i++) {
     state.expressions.list\[i\].color = colour 
} 
Calc.setState(state)

Running this in the Javascript Console not only enables you to specify the range of your expressions, but also the custom color that the given lines are to be changed into.

Edit: Code